Many proposals have been made to reinforce, strengthen, or otherwise beneficially alter the properties of cementitious mixtures by applying and/or incorporating various types of fibrous components, including asbestos, glass, steel, as well as synthetic polymer fibers to aqueous based concrete mixes prior to the curing of the concrete. The types of polymer fibers in use or proposed for use include those composed of natural and synthetic compositions.
As is evident in the prior art, individual fibrous components are well known in terms of their performance modifying attributes. Relatively large diameter fibers, for example, can be added to a cementitious mixture such as a wet concrete blend, dispersed in the blend by mechanical agitation, followed by pouring and curing of the concrete. Large diameter staple fibers serve to reinforce the concrete after it has been cured, by providing additional tensile strength and minimizing impact damage and crack propagation. Small diameter staple fibers, typically having a relatively high surface area, are commonly added to concrete mixes in order to reduce the development of small cracks in the concrete during the curing period. The problem of crack development is known to occur as a result of uneven curing of the concrete.
Staple length fibers, as have been conventionally used, are provided in the same form as such are manufactured from the fiber formation line, which included agglomerates of various size and weight, tangles or knots of intermingled staple fibers, and numerous individual staple fibers that are in and of themselves prone to release randomly. More recently, a unitized fibrous construct which comprises a plurality of oriented reinforcing fibrous components has been introduced, such a construct is described in co-pending application Ser. No. 60/442,574, incorporated herein by reference. The fibrous components are cut to a predetermined and finite cut length upon formation and remain in a plural parallel form until such point the unitized fibrous substrate is incorporated and subjected to mechanical agitation during preparation of a cementitious blend or mixture. The unitized fibrous construct is endowed with inherent and improved dispensability and dispersability of the associated reinforcing fibrous component into organic or inorganic cementitious matrixes, such as concrete, mortar, plaster, etc.
While the functional performance of the reinforcing fibrous components is beneficial, the means for the quantitative measurement and physical addition of the reinforcing fibrous components into a cementitious mixture is not without issue. U.S. Pat. No. 5,947,645 and No. 5,931,610, both incorporated herein by reference, disclose a fiber dispensing system for storing and delivering fibrous material which includes a housing for receiving and storing the fibrous material. The fibers are guided out of the housing by fingers that are positioned in a helical or spiral manner along an axle within the housing. The fingers rotate, traveling through the fibers, removing them from the housing and dispensing them in a steady stream into a cementitious mix. An alternate method for dispensing fibers is described in U.S. Pat. No. 5,529,247, also incorporated herein by reference. This method uses an apparatus comprising a U-shaped screen to prevent clumps of fiber from passing through into the cementitious mix.
The aforementioned prior art is not conducive to dispensing unitized fibrous constructs. Although a screen may be altered to pass the unitized bundles, an impact problem still exists. The use of screens, grids, and rotating fingers in dispensing unitized fibrous constructs is problematic due to the constructs colliding with the screen or grid. Such an impact would cause the unitized fibrous constructs to burst prior to being dispensed into an aggregate mix. An unmet need exists for a dispensing system that will transport and dispense unitized fibrous constructs in tact into a cementitious mixture.